How to use ASSIMP library to 3D model format

...and background of the problem

Using the assimp library you want to import the original 3D model and export the 3D model in a new format

phenomenon and occurrence background, please write the first error message

found the explanation of the official documentation unreadable. It is probably not for beginners.

Insert code with code block function, do not paste screenshot. Answer rate decreased by 50% without using code blocks

#pragma once

#include <assimp/Importer.hpp>      // C++ importer interface
#include <assimp/scene.h>           // Output data structure
#include <assimp/postprocess.h>     // Post processing flags

#include <iostream>
#include <string.h>
using namespace std;

#define print(x) cout << x << endl
#define printV2(x) cout <<"("<<x[0]<<", "<<x[1]<<")"
#define printV3(x) cout <<"("<<x[0]<<", "<<x[1]<<", "<<x[2]<<")"
#define printColor(x) cout <<"("<<x.r<<", "<<x.g<<", "<<x.b<<")"
#define len(x) sizeof(x)/sizeof(x[0])
#define type(x) typeid(x).name()

#include <assimp/Importer.hpp>      // C++ importer interface
#include <assimp/scene.h>           // Output data structure
#include <assimp/postprocess.h>     // Post processing flags
#include <assimp/IOStream.hpp>

// 这部分主要是导入3D模型文件

bool DoTheImportThing(const std::string& pFile) {
    // Create an instance of the Importer class
    Assimp::Importer importer;

    // And have it read the given file with some example postprocessing
    // Usually - if speed is not the most important aspect for you - you'll
    // probably to request more postprocessing than we do in this example.
    const aiScene* scene = importer.ReadFile(pFile,
        aiProcess_CalcTangentSpace |
        aiProcess_Triangulate |
        aiProcess_JoinIdenticalVertices |
        aiProcess_SortByPType);

    // If the import failed, report it
    if (nullptr != scene) {
        print(importer.GetErrorString());
        print("导入模型失败");
        return false;
    }

    // Now we can access the file's contents.
    print("成功获取scene 导入模型成功");

    // We're done. Everything will be cleaned up by the importer destructor
    return true;
}

// 这部分主要是构造IO逻辑

// My own implementation of IOStream
class MyIOStream : public Assimp::IOStream {
  friend class MyIOSystem;

  protected:
      // Constructor protected for private usage by MyIOSystem
      MyIOStream();

  public:
      ~MyIOStream();
      size_t Read(void* pvBuffer, size_t pSize, size_t pCount) { ... }
      size_t Write(const void* pvBuffer, size_t pSize, size_t pCount) { ... }
      aiReturn Seek(size_t pOffset, aiOrigin pOrigin) { ... }
      size_t Tell() const { ... }
      size_t FileSize() const { ... }
      void Flush() { ... }
};

// Fisher Price - My First Filesystem
class MyIOSystem : public Assimp::IOSystem {
    MyIOSystem() { ... }
    ~MyIOSystem() { ... }

    // Check whether a specific file exists
    bool Exists(const std::string& pFile) const {
        ..
    }

    // Get the path delimiter character we'd like to see
    char GetOsSeparator() const {
        return '/';
    }

    // ... and finally a method to open a custom stream
    IOStream* Open(const std::string& pFile, const std::string& pMode) {
        return new MyIOStream(...);
    }

    void Close(IOStream* pFile) { delete pFile; }
};

// 现在您的 IO 系统已实现，通过调用将其实例提供给 Importer 对象

Assimp::Importer::SetIOHandler().


// 这部分主要是导出3D模型

bool exporterTest() override {
    ::Assimp::Importer importer;
    ::Assimp::Exporter exporter;
    const aiScene* scene = importer.ReadFile(ASSIMP_TEST_MODELS_DIR "/OBJ/spider.obj", aiProcess_ValidateDataStructure);
    exporter.Export(scene, "obj", ASSIMP_TEST_MODELS_DIR "/OBJ/spider_out.obj");
    return true;
}

>

Running result and detailed error content

The code given in the official documentation of

may contain a lot of pseudo-code. As a beginner, I can't understand it at all. There are many syntax problems and unknown problems.

My answer ideas and tried methods, and those who don't write their own ideas, the answer rate drops by 60%

I can only solve it one by one, but some of them are not syntax problems, some of them are third-party library Settings that can't be solved in a short time.